Transfer of carbon and nutrients from the upper ocean to the deep sea largely results from biological processes (sinking particles and active transport) and their linkage to physical processes (mixing of dissolved organic matter—DOM). The least known component of the "biological pump" is the active transport of carbon and nutrients by diel vertical migration of zooplankton. We measured respiration and excretion rates of common vertically migrating zooplankton at the Bermuda Atlantic Time-series Study (BATS) station in the Sargasso Sea. The inclusion of dissolved organic carbon and nitrogen excretion in this study builds on previous research on active transport of inorganic carbon and nutrients and allows a direct assessment of the role of zooplankton in the production of DOM used in midwater microbial processes. Organic excretion represents a significant augmentation to the vertical flux that has already been documented for inorganic carbon and nitrogen (CO₂ and NH₄) flux by migrant zooplankton. In addition, migratory fluxes are significant compared to other transport processes (sinking particles and physical mixing of DOM). During most of the year when deep mixing does not occur, diel migration by zooplankton likely provides an important supply of DOM to the deeper layers that is available for use by the microbial community. New estimates of active transport by migrants may help resolve observed imbalances in the carbon budget at BATS, but the magnitude is highly dependent on the biomass of the migrating community. Other zooplankton-mediated fluxes (production of fecal pellets, molting, and mortality at depth) will also be discussed.

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